Hydraulic brake failure preventer



Feb. 18, 1941. w. H. GILLE I HYDRAULIC BRAKE FAILURE PREV EN'I'ER 3 Sheets-Sheet 1 Filed Oct. 25,- 1939 Invenior Aiiorneys' Feb. 18, 1941. w. H. GILLE 2,232,601

HYDRAULIC BRAKE FAILURE rnsvsuwaa Filed Oct. 25, 19:59 sands-sheet 2 AZZorneys Feb. 18, 1941.

HYDRAULIC BRAKE FAILURE PREVENTER W. H. GILLE Filed 001:. 25. 1939 3 Sheets- 811091: 3

Aiiorneys Patented Feb. 18 194i UNITED STATES PATENT- OFFICE.

' nrpaauuc imai rfr 'fir manranvnmn 3:32 :11. 301,226

17 Claims.

My invention relates to hydraulic brake operating systems such as are used in automotive vehicles and particularly to apparatus for preventing failure of such systems due to fluid leaks therein. t

The usual hydraulic brake system includesa pedal operated master unit for production of fluid pressure in communication with a conduit having'branch conduits leading to respective individual fluid pressure actuated brake shoe operating units. In such a system a fluid leak in any one of the brake shoe operating units or branch conduits will not only result in loss of a quantity of fluid but will prevent production of pressure in the system and thus render -the entire system inoperative for braking p p ses. The-possibility of a brake systemfailure of this kind obviously creates a serious hazard in the operation of a vehicle equipped with a. hydraulic brake system.

Various devices have been designed for pre-. venting complete failure of a hydraulic brake system in the event that a fluid leak occurs in any branch conduit or individual brake operating unit. One such device is shown in Fig. 7 of Patent No. 1,967,383, issued to 'I'urgot on July 24,

1934. This device includes in a chamber it normally centered member 5 serving asa pair of pistons which will shift toward one of the other of ports at the respective ends of the chamber when there is an unbalance in fluid flow through the respective parts and will function as a valve to close the one of said ports through which the greater-amount of fluid is flowing. 'Such a de-.

vice, which may and will hereinafter be referred to as a balanced valve device, will function to block flow offluid to a leaky'part of a hydraulic brake system but may also, at times, due to'being jarred, to momentary disturbances in the system or to other causes, operate to block flow of fluid to part of the system when there is no leak in the system and such unnecessary operation hence constitutes a disadvantage rather than an advantage. v

A general object of my invention is to provide a balanced valve safety device constructed to ob viate the possibility of unnecessary. operations thereof. a i

A more specific object is to provide such a device including means which normally restrains the device from operating and which will release the device for operation only responsive to lackof normal braking pressure in the system when the piston of the master unit has been moved to a position whereat normal pressure is ordinarily attained.

Another object is to provide such a device which n is automatically self adjusting to compensate for he usual gradual change in the position of the piston of the master unit whereat normal braking pressure is attained.

. 5 A further object is to provide such a device of Figs. 2 a nd 3 are more or less diagrammatic views of portions of respective hydraulic brake systems wherein respective variations of an entirelymechanical form of my device are incorporated;

Figs. 4 and 5 are more or less diagrammatic views of portions of respective hydraulic brake systems wherein respective variations of a partially hydraulic form of my device are incorporated; and

Fig. 6 is a diagrammatic representation of. a system of the type wherein my device would be incorporated.--

Referring to the drawings Fig. 6 illustrates diagrammatically a hydraulic brake system for antomotive vehicles including a brake pedal 1 connected through a rod 8 to the piston ofa master cylinder unit 9. The outlet of the master cylinder 9 is connected through a conduit III to a safety device ll of the balanced valve type. "The outlet ports of the safety device I! are connected through conduits l2 and I! to respective independent pairs of individual brake shoe operating cylinder units It. My device is designed for use inconnection with the brake pedal master cylinder unit and safety device of such a system.

Fig. 1 illustrates a very simple form of my devicenot including the refinements and self-adjusting features provided in the devices of Figs. 2 to 5 inclusive. Fig. 1 includes a master cylinder l5 having therewithin a piston l6 connected through a rod II to an arm l8a carried by a brake pedal 18. The master cy nder I! may be equipped with the usual flui reservoir lid associated therewith in a conventional manner. The pressure chamber of the master cylinder I5 is connected through a conduit I! to the interlor of a balanced valve safety device 20. The safety device 2|) has fluid, outlet ports 2| in respective ends thereof adapted to be connected as through the conduits 22 to respective groups of brake shoe operating cylinder units. Between the outlets 2| isa normally centered longitudinally movable member 23 having at its respective ends enlarge portions 23a adapted for'closing the outlet ports 2|. The member 23 through its enlarged end portions 23a constitutes twin,

. apertured to accommodate extension of the member 23 therethrough. A portion 25a of the plunger 25 defining the central aperture thereof and situated above the member 23, as viewed in Fig. 1, is V-shaped for engagement in the groove 24. A spring 26 is provided for pressing the V-shaped part of the plunger 25 into engagement with the groove 24. The lower end 251) of the plunger .25 extends to a point outside of the limits of the safety device 20. The plunger 25a constitutes means for normally retaining the member 23 in centered position, and may be shifted upwardly to release the member 23 for longitudinal movement.

Means is provided for shifting the plunger 25 out of retaining position responsive to movement of thebrake pedal l8 beyond the position thereof whereat full braking pressure is normally obtained. For this purpose the hub portion l8b is provided with an arm |8c which extends to a point beneath the lower end'25b of the plunger 25 and moves toward the plunger 25 responsive to brake applying movement of the pedal l8. For purposes of adjustment the free end of the arm |9c may be provided with a screw 21 as shown, the upper end of which is aligned with the lower end 25b of the plunger 25. The screw 21 should be so'adjusted as to just make contact with the lower end 25b of the plunger 25 as the brake pedal |8 reaches the position. thereof whereat full brak ng pressure is ordinarily produced.

Should a leak develop in one of the conduits 22 or a brake shoe operating unit served thereby pressure on the pedal l8 will result in a certain amount of fluid escaping through the leak. The pedal l8 will,therefore, move through a greater distance than normal with the result that the screw 21 will raise the plunger 25 to releasethe member 23 for longitudinal movement. The usual operation of the member 23 will then occur as in any balanced valve safety device of this type and the outlet port 2| in communication with the leaky portion of the system will be closed. Continued brake applying movement of sult of momentary disturbance in the braking system,.larring or other conditions occuring during a braking operation. It should be apparent that my retaining means prevents such unnecessary and undesirable operations of the safety device and yet permits normal operation of the safety device whenever a leak does occur in the system. g

Figs. 2 and 3 illustrate a form of the above described device including -a mechanical means for adjusting the device to compensate for the grad-' 'ual change in the position of the brake pedal whereat full braking pressure will be obtained, this gradual change being the result of wear in mechanical portions of the system particularly wear of the friction surfaces of the brake shoes.

In Fig. 2 a brake pedal 28 is pivotally mounted at 29 and has a lower arm 36 connected through a rod 3| attached to a master piston 32 working in a master cylinder 33. The outlet 33a of the master cylinder 32 is connected'to the inlet 34a of a balanced valve safety device 34. The safety device 34 has respective outlets 34b between which a longitudinally movable normally centered piston and valve member 35 is situated. The member 35 is similar to the member 23 of Fig. 1 and. is provided with retaining means in the form of a plunger 36 which is generally similarto the plunger 23 of Fig. 1. The plunger 36 is mbvable to the left out of retaining position and is urged to the right by suitable means such as a spring 31. The left-hand end of the plunger 36 extends to a point outside of the limits of the safety device 3! to be accessible for outward pulling thereof to shift the plunger 36 out of retaining position.

At a point a moderate distance above the point 29 at which the brake pedal 28 is pivoted the brake pedal is apertured and internally screw threaded and carries in screw threaded engage ment therein a screw 38. The rear end of the screw 38 is connected through a swivel connection element 39 and a helical tension spring 40 to the forward end of the plunger. 36. The forward end of the screw 38 is provided with a crown ratchet 41. Forward of the ratchet 4| is a pawl 42 pivotally mounted on a fixed pivot 43. The working end of the pawl 42 is situated for engagement with the teeth of the ratchet 4| at the side thereof farthest from a viewer of Fig. 2. Rearward movement of the pawl 42 is limited by means of a fixed stop element 44 and a helical tension spring 43 is provided for maintaining rearward pressure on the pawl 42.

Immediately forward of the brake pedal arm 28 is a rearwardly facing crown ratchet 46 mounted on the screw 38 for longitudinal movement of the screw therethrough. A key 41 and suitable key-ways in the screw 38 and ratchet 46 is provided to prevent rotation of the ratchet 46 relative to the screw 38. Forwardly of the ratchet 46 is a centrally apertured member 48 mounted on the brake pedal arm 28 and frictionally engaging the forward side of the ratchet 46. Immediately rearwardly of the ratchet 46 is a pawl 49 swingably mounted on a fixed pivot 50 and situated for engagement of its working end with the teeth of the ratchet 46 on the side thereof farthest from a viewer of Fig. 2. A fixed stop element 5| is provided to limit forward movement of the pawl 49 and a helical tension spring 52 is provided to maintain upwardly directed pressure on the pawl 49. I

When the brake pedal 28 is pressed forwardly in a brake ap lying operating the pawl 42 moves on the ratchet 4| to screw the screw 38 toward the plunger 36, and when the brake pedal is released and moves toward its normal nonbraking position the pawl 49 moves on the ratchet 46 to screw the screw 38 away from the plunger 36. The proportions. of the ratchets 4| and 46 and the pawls 42 and and the positions of the pivots 43 and 56 and stops 44 and are so selected that the screw 38 will be screwed through approximately the same distances in opposite directions during each complete cycle of brake applying and brake releasing movement of the pedal 28. However, if wear takes place in the brake shoes, the pedal will be depressed through gradually increasing distances and hence the pawl 42 and ratchet'4l will tend to screw the screw 38 to the right relative to the brake pedal arm 36 to a very slight greater degree than the pawl 46 and ratchet 46 screws the screw 38 to the left. In this manner the device is con-' stantly re-adjusted to compensate for normal wear in the braking system and is capable of releasing the safety device for operation thereof whenever during a given braking operation the pedal 28 is depressed to an appreciable greater distance to obtain full braking pressure than was the case in the preceding braking operation.

Fig. 3 illustrates a slightly different arrangement of parts similar to those constituting the master cylinder 58.

device of Fig. 2. The structure of Fig. 3 includes a brake pedal 53 mounted on a pivot 54 and having a lower arm 55 connected through a bar 56 to a master piston 51 working in a master cylinder 58. A balanced valve safety device 59 is provided having a fluid inlet 59a adapted for connection to afluid outlet 5811 provided in the The safety device 53 includes fluid outlets 59b in respective ends thereof between which is situated a piston and valve member 68 similar to the member 23 of Fig. 1. At the ends of the member 68 are provided helical compression springs 6| proportioned for exerting only very slight pressures for the purpose of returning the member 60 to a centered position thereof following an operation of the member 60 caused by leakage ina portion of the system with which the safety device 58 is used. The member 60 is provided in its central portion with a V-shaped groove 6011. similar to the groove v24 of the member 23 in Fig. 1. A plunger 62 is provided having a V-shaped inner end 62a adapted for engagement in the groove 68a. Ahelical compression spring 63 is arranged for normally holding the V-shaped' end62a of the plunger 62 in engagement in the groove 60a. The outer or right-hand end of the member 62 projects outwardly of the safety device 59 and may be pulled outwardly to shift the plunger 62 out of its retaining position. The bar 56 is provided with a downwardly projecting apertured bracket 64 wherein a bearing bushing 64a is provided. A rearwardly facing crown ratchet 65 is disposed to the right of the bracket 64 and has a forwardly extending journal element 65a journalled in the bushing 64a. The forward end of the journal element 65a is externally screw threaded and provided with a nut 66. A dished centrally apertured resilient friction element 61 is interposed between the nut 66 and the bracket 64 under pressure. An upstanding lug 68 is formed on the upper side of the bar 56 at a point somewhat rearwardly of the'ratchet 65. The lug 68 carries a pivot 68 on which-is mounted a bell crank 18 having a forwardly projecting arm a and a downwardly projecting arm 10b. A pawl H is pivotally mounted on the free end of the forwardly projecting arm 10a in depending relation therewith. The free end of the pawl ll projects upwardly and forwardly and is positioned for engagement with the teeth of the ratchet 65 5 at the side thereof nearest 9. viewer of Fig. 3. A helical tension spring 12 is provided for maintaining forwardly directed pressure on the pawl H. The inner side of the master piston 5'! is recessed to form an auxiliary cylinder 13 hav- 10 ing an axis parallel to the bar 56. An auxiliary piston I4 is disposed in the recess 13 and is connected by means of a rod to the free end of the lower arm 18b of the bell crank 10. A helical compression spring 14a is interposed between the piston 14 and the crossed end of the recess 13. A small vent passage 16 is formed in the master piston 51 leading from the inner end of the recess I3 to the atmosphere. The piston 14 will be shifted forwardly responsive to pressure within the master cylinder 58 and will function to operate the pawl II for clockwise rotation of the ratchet 65 as viewed from the right of Fig. 3. The distance to which the piston 14 will be moved and consequently the extent to which the ratchet 65 will be rotated will be in proportion to the pressure developed within the master cylinder 58. The ratchet 65 and the journal element 65a thereof are axially apertured and internally screw threaded. A screw 11. is screw threadedly carried, in the aperture of the ratchet 65 and journal element 65a. The forward end of the screw 11 is connected to the rear end of the plunger 62 of the safety device 63 by suitable means such as a chain 18 and a swivel element I9. The rear end of the screw 17 isprovided with a rearwardly facing crown ratchet 88 immediately forwardly of which the material forming the screw 11 is not provided with screw threads. Associated with the unthreaded portion of the screw member 11 is a member 8| encircling the same in frictional engagement therewith. The upper end of the member 8| is bifurcated and straddles the lower portion of the bar 56 so as to be slidable therealong but retained thereby against rotation about the axis of the screw 11. A collar 82 is provided on the screw 11 immediately forwardly of the frictional member 8|. Rearwardlyof the ratchet 80 a pawl 83 is provided mounted on a fixed pivot 84 and forwardly pressed-by means of a helical tension spring 85. A fixed stop element 86 is provided to limit forward swinging movement of the pawl 83. The pawl 83 is situated for engagement with the teeth of the ratchet 86 at .the side thereof nearest a viewer of Fig. 3 responsive to a brake applying movement of the bar 56. 7

As the pedal 53 is moved forwardly in brake applying operation the piston 14 will be actuated by pressure within the master cylinder 56 to rotate the ratchet 65 in such direction as to move the screw I1 linearly rearwardly relative to the bar 56. During the above mentioned brake ap- 'plying movement the ratchet 80 will come into engagement with the pawl 83 and will thereby be operated to screw the screw 1] forwardly relative to the bar 56. The various parts of the device are so proportioned that the forward and rearward movements of the screw 11 produced through the action of the pawls H and 83 on theratchets 65 and 80 will ordinarilybe equal and hence cancel each. other. However, as wear in the system, such as wear of the brake shoes, takes place the pedal 53 will be pressed forward to gradually increasing distances in order to reach positions wherein full braking pressure will be produced. These increasing distances will cause the pawl 83 to rotate the ratchet 88 through a very slight greater angle than the ratchet 85 is rotated during a cycle of brake operation and hence the screw 11 will be very gradually shifted forwardly in accordance with wear in the system. The plunger 83 will thus not be retracted from retaining position by normal braking operations even after considerable wear has taken place in the system, but will be operated to release the member 68 in response to any movement of the brake pedal 53 through a substantially greater distance in one brake operating cycle than in the preceding brake operating cycle in producing full braking pressure.

It is to "be noted that in each of the above described embodiments of my invention lost motion means is provided between the brake pedal and the shiftable retaining means of the balanced valve safety device. In the form of Fig. 1 the grip between the screw 21 and the plunger 25b provides lost motion effect. In Fig. 2 the tension spring 48 provides lost motion effect. In Fig. 3 the chain 18 provides lost motion effect.

Figs. 4 and 5 illustrate a type of my device wherein hydraulic means is interposed between the brakepedal and the shiftable retaining means of the safety device.

Fig. 4 shows a structure including a master piston 81 operating in a master cylinder 88 and provided with a shank 81a which may be connected to a brake pedal in a manner similar to that illustrated in any of Figs. 1 to 3 inclusive.

A balanced valve safety device 88 is provided and the exterior portion thereof may be formed integrally with the head portion of the master cylinder 88 as shown. The fluid inlet 88a. of the safety'device 88 communicates with thepressure chamber 88a of the master cylinder 88 through a passage 88. The safety device 88 is provided with respective outlet ports 88b adapted for connection by means of conduits such as the conduits 8| to independent groups of brake shoe operat ing units., The normally centered longitudinally shiftable piston and valve member .82 of the safety device 88 is .generally similar to the member 23 of Fig. 1, but preferably is of square cross section and provided with a recess in the upper side thereof for receiving a suitable retaining means. Each end of the safety device 88 is provided with a plunger 83 for the purpose of inserting the member 82 in its centered normal position following an operation of the member 82.

Helical compression springs 84 are provided'for maintaining the plungers 83 in retracted position. -An auxiliary cylinder 85 is provided on the outside of the head of the master cylinder 88a and may be formed integrally'therewith preferably in co-axial relation therewith. The auxiliary cylinder 85 is provided with a detachable head 85a secured to the remainder of the auxiliary cylinder 85 by suitable means such as the screws 88. Working within theauxiliary cylinder 85 is an auxiliary piston 81'having an operating shank 81a projecting through a suitable aperture in the head of the master cylinder 88 into the pressure chamber 88a of the master cylinder 88. A helical compression spring 88 is placed between the piston 81 and the head a of the auxiliary cylinder '85. The lefthand or free end of the shank 81a is provided with an axially movable plunger 88 having a centrally apertured contact plate 88a secured to the outer endthereof by suitable ends such "as the screw I88. A helical compression spring I8I is provided for yieldingly maintaining the plunger 88 in outwardly projected position. A brake element I82 working on the shank 81a. is contained in a suitable recess I83 formed in the head of the master cylinder 88. The brake element I82 has a push rod 182a extending outwardly thereof radially with respect to the shank 81a whereby the brake element I82 may be guided in movement thereof radially with respect to the shank 91a. A helical compression spring I84 is provided'i'n the recess I88 for yleldingly holding the brake element I82 in braking relation with the shank 81a. Ayent. duct I85 is provided communicating between the recess I03 and the pressure chamber 88a of the master cylinder 88. The push rod N21: is sli ably extended through a suitable aperture form of the master cylinder 88 lying radially outwardly of the recess I83. A radially outwardly opening recess I85 containing the free end of the push rod I820. is formed in the head of the master cylinder 88. The outer end of the recess I88 is closed by a defiectable diaphragm I81, the central portion of which is secured to the free end of the push rod I82a by means of a screw I88 and washers I88 and H8, the marginal portion of which is secured and sealed to the head of the master cylinder 88 by means of a ring III which is anchored to the head of a master cylinder 88 by suitable means such as the screws H2. A passage H3 is provided communicating between the recess I88 and the pressure chamber 88a of the master cylinder 88 so that the diaphragm I81 will be subjected at its inner side to the pressure developed in the pressure chamber 88a whereby such pressure will deflect the diaphragm I81 outwardly to shift the brake element I82 out of braking relation with the shank 81a.

For engagement in the recessed portion of the upper side of the safety device member 82 a plunger I84 is provided. The plunger H4 extends radially relative to the member 82 and is movable radially thereof. The medial portion of the retaining element H4 is longitudinally slidably carried in a guide I I5 therefor formed in the structure lying between the safety device 88 and the head of .the master cylinder 88. The upperend of the retaining element H4 carries a piston H8 working in a cylindrical chamber H1 provided therefor. A helical spring H8 is provided in the upper portion of the chamber H1 to yieldably retain the piston H6. and retaining element H4 in a downwardly pressed position. The

upper portion of the chamber I I1 communicates in a portion of the head I Accordingly this bleed passage cylinder. 85 will work on the retaining means 1 piston H5 to retract the retaining means out of retaining relation with the balanced valve member 82 of the safety device 88.

Such pressure will be developed Within the auxiliary cylinder. 85 when brake applying movement of the master piston 81 is-communicated to the shank 81a, The shank 81a will normally be held by the brake I02 in such position that the plate 990. will be contacted by the master piston 81 which is before the piston 81 has moved The last portion of braking movement of the piston 81 will be accompanied by movement of the V plunger 99 relative to the shank 91a against the pressure of the spring IOI.. Just before the spring IOI has been sufficiently compressed to overcome the pressure of the spring 98 of the auxiliary piston 91 and the pressure of the spring II8 hydraulically communicated to the piston 91 full braking pressure will have been obtained within the pressure chamber 88a of the master cylinder 88, the brake I02 will have been released due to development of pressure in the pressure chamber 88a approximately at the time when the piston 81 engages the plate 99a. During each braking operation the piston 91 and shank 91a will be disposed between the springs 98 and IOI with the spring IOI backed by the master piston 91. Since the brake I02 will at such time be in released position the auxiliary Gil piston 91 and shank 91a will take a position corresponding to the position of the master piston 81 at which full braking pressure is obtained.

When the brake pedal starts on its brake releasing movement the piston 81 will start moving to the left and a sudden drop in pressure in the pressure chamber 880. will result, with the secondar result that the brake I02 will be applied to the shank 91a to retain the auxiliary piston 91' and shank 91a in the positions which they have assumed during the braking operation. Thus the shank 91a will not follow the master piston 81 in a brake releasing movement thereof. In

a case where a brake operation is attempted when a leak has developed in apparatus connected to the conduits 9|, the master piston 81 will not have been able to producefull braking pressure in the pressure chamber 88 before the master piston 81 has engaged the plate 99a and compressed the spring IM to such extent that the shank 91a. and piston 91 will have been pushed to the right by the master piston 81 to eifect release of the retaining means II4. With the posto close off the one of the outlet ports 8% of the safety device 89 leading to the leak. After this has occurred further movement of the master 7 piston in a brake applying position will build up pressure in the pressure chamber 83a so that the pressure produced will be applied to the brake operating units served through the remaining one of the outlet ports 89b of the safety device 89. Thus it will be seen that the balanced valve member 92 will be retained in centered position at all times when operation'of the safety device is unnecessary but will ,be retracted whenevera leak exists in the system at the time of a braking operation. It will also be seen that the piston 91 will at all times be automatically repositioned to compensate for wear at the brake shoes of the system. The bleed passage I2I will permit equalization of the pressures within the auxiliary cylinder 95 and within the master cylinder 88 for all small or slow movements of the piston 91 without permitting retraction of the 1'75 retaining element H4. The bleed passage I2! is, however, too small to impair retraction of the retaining means II4 when the piston .91 is quickly moved through a substantial distance as" it will be in cases where a leak exists in the system at the time of a braking operation.

The form of the device shown in Fig. 5'ineludes numerous ones of the elements comprised in the structure of Fig. 4 somewhat differently arranged. The device of Fig. 5 includes a master cylinder I22 having a master piston I23 therewithin on which is a shank I24 which may be connected to a brake pedal in a manner similar to that shown in any one of Figs. 1 to 3 inclusive. A safety device I25 similar to the safety devices in the previously described structures is associated with the head I22a of the master cylinder I22. The safety device I25 has respective outlet ports I25a in the ends thereof between which is located a normally centered longitudinally movable balanced valve member I26 similar to the balanced valve member 23 described in connection with the device in Fig. 1. The exterior portion of the safety device I25 may be formed integrally with the master cylinder head I22a and is positioned with the longitudinal axis of the member I26 disposed normal to the axis of the master cylinder I22. Ports I21 are formed in the cylinder head I22a to establish communication between the interiors of the master cylinder I22 and the safety device I25. The central portion of the shiftable valve member I25 has formed therein a V-shaped annular groove I260 suited for engagement of a retaining ele- I ment therein. A retaining element I28 which is similar to the retaining element 25 of the structure of Fig. 1 is carried in suitably arranged portions of the safety device I25 so as to be engageable with the annular groove mm. A helical compression spring I29 is provided for in engagement in the groove I26a. The lefthand end of the retaining element I28 extends into the interior of the master cylinder I22 and may be pressed to the right to be disengaged from the shiftable valve member I26.

The master piston I23 is recessed on the side thereof toward the cylinder head I22a to form a piston receiving cylinder I30. An auxiliary piston I3I is placed in the recess or cylinder I30. An axially extending passage I3I is formed in the piston I3I and extends between the front and rear ends thereof.- Adjacent the end of the piston I3I nearest the cylinder head I32a the passage I3I is of enlarged diameter and contains an enlarged inner end portion I32a of a plunger I32 which extends outwardly of the piston I3I. A helical compression spring I33 is placed inwardly of the enlarged portion I32aof the plunger and within the enlarged portion of the passage I 3| so as to yieldably maintain the plunger I32 in an outwardly projected position thereof. The free end of the plunger I32 is provided with an enlarged element I321). A fluid passage I34 is formed in the piston I3I and extends from the outer end thereof to a portion of the passage I3I closely adjacent the inner end of the plunger I32. With the plunger I32 in projected position the passage I34 and the passage closed end of the cylinder I 30 and the inner piston I-3I in braking relation therewith. A helical compression spring I33 is provided inside the recess I33 to yieldably retain the brake element I31 in braking relation with the piston I3I. -A recess I33, is formed on the outer periphery of the master piston I3I and the push rod Illa of the brake element I31 extends thereinto. The outer side of the recess I33 is closed by a diaphragm I40 formed of resilient materialso as to be deflectable. The center of the diaphragm I43 is secured to the free end of the push rod I31a as by means of a screw HI and a washer I42, and the marginal portion of the diaphragm I40 is secured to the master piston I23 by means of a ring I43 attached to the master piston as by screws I44. The recess I33 is in communication with the pressure chamber of the master cylinder I32 through a passage I45 formed in the master piston I23.

During a brake applying movement of the master piston I23 fluid pressure within the master cylinder I22 will release the brake element I31 so that the spring I35 may project the piston I3I toward the head I22a. During this operation fluid will flow through the passages I34 and I3I into the inner portion of the. recess or cylinder I30. The enlarged end I32b of the plunger I32 will engage the retaining element I23. The spring I33 is proportioned to be secured to the spring I29 and hence the slight further movement of the master piston I23 to the position thereof whereat full braking pressure is obtained is accompanied by compression of the spring I33 rather than shiftingof the retaining element I28. If, due to a leak in the brake system, the movement of the master piston I23 is excessive, the enlarged rear portion I32a oi the plunger I32 will have become displaced inwardly to such a point as to block the passage I34 and hence lock the auxiliary piston I3I' against shifting relative to the master piston I23. Then if the-spring I33 is further compressed, the pressure thereon will become sufllcient to shift the retaining element I23 out of retaining position to permit shifting of the balanced valve I23. Following operation of the balanced valve I26 to shut off fluid to the leaky portion of the system slight further movement of the master piston will build up pressure which is applied to the portion of the brake system which has not been blocked by the valve member I23. In normal operation of the device when no leak exists in the system, the last por-- tion of a brake applying movement of the master piston I23 will be accompanied by partial compression only of the spring I33 and the position of the piston I23 whereat full braking pressure is obtained will be reached before the retaining element I23 has" been shifted. As themaster piston I23 is retracted to release the brakes, the pressure in the master cylinder I22 will be quickly diminished to a point w ere the brake element I31 will be brought to bra I g relation with the auxiliary piston I3I to restrain the same against shifting relative to the master piston I23. Thus the auxiliary piston I3I will be automatically properly positioned for use in a following brake applying operation of the device.

It is apparent that I have invented novel, effective, compact, rugged and inexpensive appa ratus for preventing failure of hydraulic brake systems due to leakage therein and at the same time preventing unnecessary operation of a balanced valve safety deuice. It is also apparent that my invented device is automatically self-adlusting to compensate for wear in a brake system such as the wear which occurs on the friction surfaces of the brake shoes.

It will, of course, beunderstood that'various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scope of my invention.

' What is claimed is:

1. In a fluid brake system having a pedaloperated master cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating hydraulic units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through'either one of said ports to cover said one port, releasable means for normally retaining said member in centered position, and means operated by the master cylinder operating pedal responsive to excessive brake applying movement thereof to release said retaining means.

2. In a fluid brake system having a pedalmember in normal position, said retaining element being shiftable out of retaining relation with said member, yieldable means for normally holding said retaining element in retaining relation with said member, and mechanism operated by the master cylinder operating pedal responsive to excessive brake applying movement thereof to'sh ift said retaining element out of retaining position.

3. In a fluid brake system having a pedaloperated master cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through either one of said ports to cover saidone port, means normally retaining said member in centered position, said retaining means being retractable out of retaining position, mechanism brake-applying movement of said pedal through a distance greater than normal. i

4. In a fluid brake system having a pedal operated mas r cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through either one of said ports to cover said one port, means normally retaining said member in centered position, said retaining means being retractable out of retaining position, mechanism for transmitting brake-applying movement of the pedal of said master unit to said retaining means for retracting the same, lost-motion means interposed in said mechanism whereby retraction extent by relatively small successive increments to compensate for gradual increase in said caused by wear.

5. In a fluid brake system having a pedaloperated master cylinder unit in communication with a safety device cylinder havingfluid outlet ports in its respective ends leading to respecrange tive independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through either one of said ports to cover said one port, means for normally retaining said member in centered positiomsaid retaining means being movable out of retaining position to release said Vmember, lost-motion means connecting the pedal of said master unit to said retaining means to effect releasing movement thereof responsive to excessive brake-applying movement of said pedal, said 10st motion means being adjustable as to the extent of lost motion therein, means operating responsive to a brake-applying movement of said pedal for increasing said extent by an increment proportional to the distance of travel of said pedal, and means operating responsive to.

a movement of said pedal for decreasing said extent by a predetermined increment.

6. In a fluid brake system having a pedaloperated master cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through either one of said ports to cover said one port, spring pressed means for normally retaining said member in centered position, said retaining means being retractable out of retaining position, a screw extending substantially in the direction of retraction of said retaining means, internally screw-threaded means screw-threadedly carrying said screw and associated with the pedal of said master unit to move in said direction responsive to movement of said pedal in a brake-applying direction, lost motion means connecting said screw to said retaining means, means for screwing said screw toward said retaining means re-' sponsive to brake applying movement of said pedal through a distance proportional to the distance of said movement, and means for screwing said screw in a direction away from said retaining means responsive to brake-releasing movement 'of'said pedal.

taining said member in centered position, said retaining means being retractable out of retaining position, a screw screw-threadedly carried by the pedal of said master unit for longitudinal movement therewith, said safety device cylinder being positioned for retractive movement of said retaining means in substantially the same line and direction as said screw, lost motion means i connecting said retaining means to said screw for retractive movement of said retaining means responsive to excessive brake-applying movement ofsaid pedal, means for screwing said screw toward said retaining means responsive to brakeapplying movement of said pedal through a distance proportional to the distance of pedal travel, and means for screwing said screw away'from .said retaining means through a predetermined distance responsive to brake-releasing movement of said pedal.

8. In a fluid brake system having a pedaloperated master cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive fluid flow through either one of said ports to cover said one port, spring pressed means for normally retaining said member in centered position, said retaining .means being retractable out of retaining position, a screw screw-threadedly carried by the pedal of said master unit for longitudinal 'movement therewith, said safety device cylinder being positioned for retractive movement of said retaining means in substantially the same. line and direction as said screw, lost motionmeans connecting said retaining means to said screw for retractive movement of said retaining means responsive to excessive brake-applying movement of said pedal, a forwardly facing crown wheel ratchet mounted on the forward end of said screw, a rearwardly inclined pawl swingable about a stationary mint and rearwardly spring pressed into engagement with said ratchet for acting thereon to screw said screw toward said'retaining element responsive to brake-applying movement of said pedal and to a degree proportional to the distance of pedal travel, a rearwardly facing crown wheel ratchet mounted on said screw in non-rotatable but axially slidable relation therewith, means restraining said last-mentioned about a stationary point and forwardly spring pressed into engagement with said last mentioned ratchet for acting thereon to screw said screw through a predetermined distance in a direction away from said retaining element responsive to brake-releasing movement of said pedal.

9. In a fluid brake system having respective independent brake operatingcylinder units connected to ports in respective ends of a safety device cylinder containing a normally centered member shiftable responsive to excessive fluid flow through either one of said ports to cover said one port, and having a master cylinder connected to the interior of said safety device cylinder and containing a master piston'provided' with a shank connected to a brake pedal, spring pressed means normally retaining said member in centered position and retractable out of retaining position, a screw extending parallel-to said shank, an internally screw threaded sleeve carried on said screw, an apertured' projection on said shank wherein said sleeve is journalled, enlarged elements on said sleeve at opposite sides of said projection, said safety device cylinder be-' ing positioned for retraction of said retaining means co-directionally with brake-applying movement of said shank, lost-motion means connecting said screw to-said retaining means, one of said enlarged elements being formed into a ratchet, a secondary cylinder communicating with said master cylinder formed in said master piston, a secondary piston in said secondary cylinder, a pawl operated by said secondary piston and working on said ratchet to rotate said sleeve for-moving said screw through a predetermined distance toward said master piston responsive to a brake-applying movement thereof, a crown atchet facing said master pistonflxed on said screw, and a pawl swingable about a fixed point inclined toward and engageable with said crown ratchet for operating the same responsive to a brake-applying movement of said master piston to screw said screw away from said master piston through a distance proportional to the distance of i friction means restraining rotation of saidscrew.-

12. In an automotive fluid braking system, a

master unit including a cylinder and a piston working therewithin together defining a pressure chamber, a safety device including a cylinder communicating with said chamber and having ports in its respective ends adapted for connection to respective brake operating cylinder units and a normally centered member within said safety device cylinder shiftable responsive to excessive fluid flow through either one of said ports to close said one port, means normally retaining said member in centered position but shiftable out of retaining condition, a series of elements between said master piston and said retaining means for communicating brake-applying movement of said master piston to said retaining means to shift the latter out of retaining condition, said series having a gap therein when said master piston is in retracted position, said gap being closed during and'responsive to brakeapplying movement of said master piston, and means yieldable within limits interposed in said series.

13. In an automotive fluid braking system, a master unit including a cylinder and a piston working therewithin together defining apressure chamber a safety device including a'cylinder communicating with said chamber and having ports in its respective ends adapted for connection to respective brake-operating cylinder units and a normally centered member within said safety device cylinder shiftable responsive to excessive fluid flow through either one of said ports to close said one port, an auxiliary cylinder and a piston therewithin a pushrod projecting into said chamber parallel to the axis thereof and from a location external thereto, the outer end of said pushrod being connected to said auxiliary piston for compressive actionthereof responsive to movement of said pushrod outwardly of said chamber yielding means on the inner end of said pushrod adapted to be engaged by said master ber in centeredposition, and hydraulic means communicating with said auxiliary cylinder and operative responsive to pressure to release said retaining means.

chambenasafetydevice including a cylinder communicating with said chamber and having ports in its respective ends adapted for connection to respective brake-operating cylinder units and a normally centered member within said safety 5 device cylinder shiftable responsive to excessive fluid flow through either one of said ports to close said one port, an auxiliary cylinder mounted on the head of said master cylinder,

a piston in said auxiliary cylinder provided 10 with a pushrod projecting into said chamber, said head being apertured to closely accommodate projection of said rod therethrough, means for normally retaining said member in centered position, said means being retractable to release said member, hydraulic means com-i municating with the pressure chamber of said auxiliary cylinder and operative responsive to pressure to retract said retaining means yielding means on the free end of said rod adapted 2 to be engaged by said master piston during a brake-applying movement thereof, a normally applied brake fon restraining longitudinal movement of said rod hydraulic means communicating with said chamber andoperative responsive to pressure to release said restraining brake, and means yieldingly urging said rod toward said master piston.

15. In an automotive ffuid braking system a master unit including a cylinder and a piston working therewithin together defining a pressure chamber, a safety device including a cylinder communicating with said chamber and having ports in its respective ends adapted for connection to respective brake-operating cylinder units and a normally centered member within said safety device cylinder shiftable responsive to excessive fluid flow through either one of said ports to close said'one port, means normally retaining said member in centered position but .shiftable out of retaining condi-' tion the inner end of said master piston being recessed to form a secondary cylinder for re-- ceiving a piston, a secondary piston in said secondary cylinder a yieldable element on the 5 end of said secondary piston toward the head of said master cylinder, an element in the head of said master cylinder positioned and arranged to be engaged and shifted outwardly by said yieldable element during and responsive go to the latter portion of a brake-applying movement of said master piston, means being connected to said shiftable element to be shifted by outward movement thereof out of retaining condition. 5

said retaining 16. In an automotive fluid braking system,

a master unit including a cylinder and a piston working'therewithin together defining a pressure chamber, a, safety device including a cyljinder communicating with said A chamber and 60 having ports in its respective ends adapted for connection to respective brake-operating cylinder units and a normally centered member within said safety device cylinder shiftable responsive to excessive fluid flow through either 65 one of said ports to ,close said one port, said safety device cylinder being situated on the outer side of the head of said master cylinder and being disposed normal to the axis thereof, means yieldingly pressed to normally retain said member in centered position, said retaining means being extended into'said 'chamber 14. In an automotive fluid braking system a and being shiftable outwardly relative to said master unit including a cylinder and a piston head out of retaining position, the inner end of working therewithin together defining a pressure said master piston being recessed to form a 75 outwardly, yieldable means on the outer end of said secondary piston for engagement with said retaining means to transmit thrust thereto from said master'piston during the latter portion of a brake-applying movement of saidmaster piston, a fluid passage running between the inner and outer ends of said secondary piston, means associated with said passage and said yieldable means for closing the former. responsive to yielding of the latter; a yieldingly pressed brake normally restraining movement of said secondary piston relative to said master piston, and hydraulic means associated with said brake and communicating with said chamber to release said brake responsive to pressure in said cham-,

ber.

17. In a fluid brake system having a pedal- ,operated master cylinder unit in communication with a safety device cylinder having fluid outlet ports in its respective ends leading to respective independent brake operating cylinder units and including a normally centered member therewithin shiftable responsive to excessive 'fluid flow through either one of said ports to cover said one port, means for normally retaining said member in centered position, said retaining means being movable out of retaining position to release said member, lost-motion means connecting the pedal of said master unit to said retainingmeans to effect releasing movement thereof responsive {to excessive brake applying movement of said pedal, said lost motibn means being adjustable as to the extent'of lost motion therein, means operating responsive to production of braking pressure for increasing said extent by a small increment, and means operating responsive to a movement of i said pedal for decreasing said extent by a predetermined increment. v

WILMS H. GIILE. 

